Motor

ABSTRACT

A motor having a rotor and a stator is disclosed. A motor having a rotor and as stator is disclosed. The rotor is a consequent-pole rotor having a rotor core, a plurality of magnets, and a plurality of salient poles. The stator includes a plurality of teeth. The stator is arranged to be opposite to the rotor with a gap along the radial direction. The gap between the stator and the rotor is set to satisfy an expression 1&lt;B/A, where A represents the shortest gap distance between the stator and the magnets, and B represents the shortest gap distance between the stator and the salient poles.

BACKGROUND OF THE INVENTION

The present invention relates to a motor having a rotor of aconsequent-pole structure.

For example, Japanese Laid-Open Patent Publication No. 9-327139discloses a rotor of a consequent-pole structure as a rotor for a motor.The rotor of the above publication includes a rotor core, a plurality ofmagnets arranged along the circumferential direction of the rotor core,and salient poles integrally formed with the rotor core. Each salientpole is located between a circumferentially adjacent pair of themagnets. The magnets function as either north poles or south poles, andthe salient poles function as magnetic poles different from the magnets.While suppressing reduction in the performance, this motor reduces thenumber of magnets to half of those in a conventional rotor in which allthe magnetic poles are formed by magnets. The motor of the publicationis therefore advantageous in terms of natural resource and cost saving.

In the meantime, since the rotor of a consequent-pole structure as inthe above publication has, in a mixed state, magnets for inducingmagnetic flux and salient poles, which do not induce magnetic flux, therotor is likely to be magnetically imbalanced. As a result, therotational performance is degraded due to vibrations increased, forexample, by the occurrence of cogging torque.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide amotor that is capable of increasing the output power while keeping thenumber of magnets in the rotor low.

To achieve the above objective and in accordance with one aspect of thepresent invention, a motor is provided. The motor comprises a rotor anda stator. The rotor includes a rotor core, a plurality of magnets, aplurality of salient poles. The magnets arrange along thecircumferential direction of the rotor core. The magnets function asfirst magnetic poles. The salient poles integrally form with the rotorcore. Each salient pole is located between a circumferentially adjacentpair of the magnets with gaps in between. Each salient pole functions asa second magnetic pole different from the first magnetic poles. Thestator arranges to be opposite to the rotor with a gap along the radialdirection. The gap is set to satisfy an expression 1<B/A, where Arepresents the shortest gap distance between the stator and the magnets,and B represents the shortest gap distance between the stator and thesalient poles.

Other aspects and advantages of the invention will become apparent fromthe following description, taken in conjunction with the accompanyingdrawings, illustrating by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1A is a schematic diagram illustrating a motor according to a firstembodiment of the present invention;

FIG. 1B is a partially enlarged view of FIG. 1A;

FIG. 1C is a partial perspective view showing a segment conductor of themotor shown in FIG. 1A;

FIG. 2A is a graph showing the relationship between the occupancy angleof the magnet poles in the motor of FIG. 1A and the torque ripple ratio;

FIG. 2B is a graph showing the relationship between the occupancy angleof the magnet poles in the motor of FIG. 1A and the average torqueratio;

FIG. 3A is a graph showing the relationship between the gap distanceratio B/A and the maximum torque ratio;

FIG. 3B is a graph showing the relationship between the gap distanceratio B/A and the torque ripple ratio;

FIG. 3C is a graph showing the relationship between the gap distanceratio B/A and the radial pulsation ratio;

FIG. 4 is a plan view illustrating a part of a motor according to amodified embodiment;

FIG. 5A is a perspective view showing a part of the stator core of themotor shown in FIG. 4;

FIG. 5B is a diagram showing the distal ends of the teeth shown in FIG.5A;

FIGS. 6A and 6B are graphs showing the characteristics of a motoraccording to a modified embodiment;

FIG. 7A is a plan view of a first lamination member forming the teeth ofa motor according to a modified embodiment;

FIG. 7B is a plan view of a second lamination member forming the teethof the motor according to the modified embodiment;

FIG. 7C is a perspective view illustrating a part of a stator core thatis formed by the first and second lamination members shown in FIGS. 7Aand 7B;

FIG. 7D is a diagram showing the distal ends of the teeth shown in FIG.7C;

FIG. 8A is a plan view of a lamination member forming the teeth of amotor according to a modified embodiment;

FIG. 8B is a perspective view illustrating a part of a stator core thatis formed by the lamination members shown in FIG. 7A;

FIG. 8C is a diagram showing the distal ends of the teeth shown in FIG.8B;

FIG. 9A is a schematic diagram illustrating a motor according to amodified embodiment;

FIG. 9B is an enlarged view of a salient pole of FIG. 9A;

FIG. 10 is a diagram showing the relationship between the salient polesand the teeth in the motor shown in FIG. 9A;

FIG. 11 is a graph showing the relationship between the rotational angleof the rotor and the cogging torque in the motor shown in FIG. 9A;

FIG. 12 is a graph showing the relationship between the cogging torqueand the groove opening angle of first auxiliary grooves formed in eachsalient pole shown in FIG. 9A;

FIG. 13 is a diagram showing the relationship between the salient polesand teeth according to a modified embodiment;

FIG. 14A is a plan view illustrating a motor according to a secondembodiment of the present invention;

FIG. 14B is a partial plan view showing a part of FIG. 14A;

FIG. 15A is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14 is at a rotational angle R1;

FIG. 15B is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14 is at a rotational angle R2;

FIG. 16 is a graph showing the relationship between the rotational angleof the rotor and the cogging torque in the motor shown in FIG. 14A;

FIG. 17 is a graph showing the relationship of W1/T and W2/T with thecogging torque ratio;

FIG. 18A is a plan view illustrating the motor of FIG. 14A;

FIG. 18B is a partial plan view showing a part of FIG. 18A;

FIG. 19A is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14 is at a rotational angle R3;

FIG. 19B is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14 is at a rotational angle R1;

FIG. 19C is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14A is at a rotational angle R2;

FIG. 19D is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 14A is at a rotational angle R4;

FIG. 20 is a graph showing the relationship between the rotational angleof the rotor and the cogging torque in the motor shown in FIG. 14A;

FIG. 21A is a plan view illustrating a motor according to a thirdembodiment of the present invention;

FIG. 21B is a partial plan view showing a part of FIG. 21A;

FIG. 22A is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 21A is at a rotational angle R5;

FIG. 22B is a partial plan view showing a state in which the rotor ofthe motor shown in FIG. 21A is at a rotational angle R6;

FIG. 23 is a graph showing the relationship between the rotational angleof the rotor and the cogging torque in the motor shown in FIG. 21A;

FIG. 24 is a graph showing the relationship between W3/T and the coggingtorque ratio;

FIG. 25 is a plan view illustrating a motor according to a fifthembodiment of the present invention;

FIG. 26 is an enlarged partial view illustrating the motor shown in FIG.25;

FIG. 27 is a graph showing the relationship between the gap distanceratio B/A and the radial pulsation ratio of the motor shown in FIG. 25;

FIG. 28 is a graph showing the relationship between the gap distanceratio B/A and the rotor imbalance force of the motor shown in FIG. 25;and

FIG. 29 is a graph showing the relationship between the gap distanceratio B/A and the torque ripple ratio of the motor shown in FIG. 25.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will now be described withreference to the drawings.

As shown in FIG. 1A, an inner rotor type motor 1 of the presentembodiment includes a substantially annular stator 2 and a rotor 3arranged radially inward of the stator 2.

The stator 2 includes a stator core 4. As shown in FIGS. 1A and 1B, thestator core 4 has a cylindrical portion 11 and a plurality of teeth 12,the number of which is sixty in the present embodiment. The teeth 12 arearranged along the circumferential direction on the innercircumferential surface of the cylindrical portion 11. The teeth 12extend radially inward from the inner circumferential surface of thecylindrical portion 11. The stator core 4 is formed by laminatinglamination members, which are plate-like members made ofhigh-permeability metal, along the axial direction. A slot ST thatextends through the stator 2 along the axial direction is formed betweeneach circumferentially adjacent pair of teeth 12. As viewed along theaxial direction, each slot ST has a rectangular cross section extendingalong the radial direction. The number of the slots ST is the same asthe number of the teeth 12 (sixty in the present embodiment). Segmentcoils 13 are inserted into the slots ST to generate a magnetic field forrotating the rotor 3. Unillustrated insulators are located between theteeth 12 and the segment coils 13.

The segment coils 13 of the stator 2 have rectangular cross section, andare wound around the teeth 12 by distributed winding of multiple phases(three phases in the present embodiment). The segment coils 13 havesegment conductors 14 each corresponding to one of the phases. As shownin FIG. 1C, each segment conductor 14 includes a slot insertion portion14 a that is located in the slot ST to extend through the slot ST alongthe axial direction (direction perpendicular to the sheet of thedrawing), a protruding portion 14 b forming the slot ST along the axialdirection, and a bent portion 14 c. Segment conductors 14 thatcorrespond to each phase are electrically connected to each other bywelding each radially adjacent pair of slot protruding portions 14 b,that is, the ends of the slot insertion portions 14 a protruding fromthe slots ST. The segment conductors 14 for each phase are formed as alead that is continuous along the circumferential direction. Eachsegment conductor 14 is formed by bending a conductor plate, andsubstantially U-shaped. In each segment conductor 14, a pair of the slotinsertion portions 14 a, which correspond to parallel linear portions,are arranged in two slots ST, between which a plurality of (six) teeth12 exist.

The rotor 3 includes a substantially annular rotor core 22, a pluralityof (five in the present embodiment) magnets 23, and salient poles 24.The rotor core 22 is made of magnetic metal and adhered to the outercircumferential surface of a rotary shaft 21. The magnets 23 arearranged on the outer circumferential surface of the rotor core 22 alongthe circumferential direction. Each salient pole 24 is located in theouter circumferential portion of the rotor core 22 and between acircumferentially adjacent pair of the magnets 23. The magnets 23function as north poles. The salient poles 24 are integrally formed withthe rotor core 22. The magnets 23 and the salient poles 24 arealternately arranged on the outer circumferential portion of the rotor 3in the circumferential direction at equal angular intervals. In thepresent embodiment, each magnet 23 is located at a position opposite to,or 180° away from, one of the salient poles 24. The rotor 3 is aconsequent pole type with ten magnetic poles that causes the salientpoles 24 to function as south poles in relation to the north polemagnets 23. The number of pole pairs of the rotor 3 is the same as thenumber of the magnets 23, in which the number of pole pairs is five inthe present embodiment. The number of the teeth 12 corresponding to asingle segment conductor 14 is determined based on the number obtainedby dividing the number of the slots by the number of the magnetic poles(the number of slots/the number of magnetic poles).

The stator 2 of the present embodiment is configured such that, when thenumber of the magnets 23 (number of pole pairs) of the rotor 3, thenumber of phases of the segment coils 13, and the number of the teeth 12are represented by p, m, and L, respectively (where p is an integergreater than one), L=2×p×m×n (where n is a natural number). Based on theexpression, the number L of the teeth 12 is set to sixty (L=2×5 (thenumber of the magnets 23)×3 (the number of phases)×2=60).

The circumferential length of each magnet 23 is slightly greater thanthat of each salient pole 24. Each magnet 23 is substantially formed asa rectangular prism having a curved outside surface 23 a and a flatinside surface 23 b. The outside surface 23 a of each magnet 23 has anarcuate shape the center of which coincides with an axis P, and isopposed to the distal ends 12 a of the corresponding teeth 12 in theradial direction. The inside surface 23 b of each magnet 23 is fixed toa fixing surface 25 provided between a circumferentially adjacent pairof the salient poles 24 in the rotor core 22. A first gap G1 existsbetween each magnet 23 and a circumferentially adjacent salient pole 24.The magnets 23 are configured such that the outside surfaces 23 a arelocated on the same circumference.

Each salient pole 24 has a sectoral cross section in the axialdirection, and has an outside surface 24 a that bulges outward in theradial direction. That is, the outside surface 24 a of each salient pole24 is curved such that its center in the circumferential directionprotrudes relative to both ends. In other words, the outside surface 24a is curved such that it approaches the radially inner end as thedistance from the center in the circumferential direction increasestoward either end in the circumferential direction. The curvature of allthe outside surfaces 24 a is the same, and symmetrical with respect tothe circumferential center.

The motor 1 of the present embodiment includes the rotor 3 and thestator 2. The rotor 3 is a consequent pole type, which is configuredsuch that the salient poles 24 of the rotor core 22 function as magneticpoles, and the stator 2 has the segment coils 13 formed by the segmentconductors 14. Compared to coils formed by winding continuous leadsabout teeth as in the conventional art, the segment coils 13 have ahigher space factor in the slots ST and thus higher output power.Accordingly, since the rotor 3 is a consequent pole type, the number ofthe magnets 23 can be kept low. The motor 1 is therefore advantageous interms of natural resource conservation and cost saving. Further, the useof the segment coils 13 as coils of the stator 2 allows the motor 1 togenerate high output power.

As shown in FIGS. 1A and 1B, the opening angle Ykθ (see FIG. 1A) of eachsalient pole 24 about the axis P is set greater than or equal to twicethe opening angle Tθ (see 1B) of the distal end 12 a of each tooth 12about the axis P (in the present embodiment, greater than or equal tofour times). That is, the distal ends 12 a of multiple teeth 12 areentirely opposed to a single salient pole 24. Therefore, the magneticflux of each salient pole 24 is allowed to smoothly flow in the radialdirection under the influence of the teeth 12 that are opposed to thesalient pole 24. This improves the magnetic balance of the rotor 3,improving the rotational performance. Specifically, the torque isimproved and the vibration is reduced. The opening angle Ykθ of eachsalient pole 24 is set to be greater than or equal to a value obtainedby multiplying the opening angle Tθ of the distal end 12 a of each tooth12 by a predetermined number. The predetermined number is preferablyequal to a number obtained by subtracting one or two from the number ofthe teeth 12 corresponding to each the segment conductor 14 (six in thepresent embodiment).

The length of each magnet 23 in the circumferential direction (occupancyangle) is defined as a first magnetic pole occupancy angle (electricalangle) θ1, which ranges from the circumferential midpoint of the firstgap G1 between the magnet 23 and one of the circumferentially adjacentsalient poles 24 to the circumferential midpoint of the first gap G1between the magnet 23 and the other circumferentially adjacent salientpole 24. The length of each salient pole 24 in the circumferentialdirection (occupancy angle) is defined as a second magnetic poleoccupancy angle (electrical angle) θ2, which ranges from thecircumferential midpoint of the first gap G1 between the salient pole 24and one of the circumferentially adjacent magnets 23 to thecircumferential midpoint of the first gap G1 between the salient pole 24and the other circumferentially adjacent magnet 23. FIGS. 2A and 2B showthe torque ripple ratio and average torque ratio when the first magneticpole occupancy angle (electric angle) θ1 and the second magnetic poleoccupancy angle (electric angle) θ2 are changed, respectively. Since thesum of the magnetic pole occupancy angles θ1 and θ2 of one magnet 23 andone salient pole 24 is an electric angle of 360° (θ1+θ2=360°), only themagnetic pole occupancy angle θ1 will be described below.

FIG. 2A shows the torque ripple ratio when the magnetic pole occupancyangle θ1 of each magnet 23 is changed. If the torque ripple when themagnetic pole occupancy angle θ1 is 180°, that is, when the magneticpole occupancy angle θ1 of the magnet 23 and the magnetic pole occupancyangle θ2 of the salient pole 24 are structurally the same, is defined as100%, the torque ripple is less than 100% when the magnetic poleoccupancy angle θ1 is in the range of 150° to 180° and in the range of210° to 270°. In the range of the magnetic pole occupancy angle θ1between 150° and 180°, the torque ripple is reduced to approximately 60%when the magnetic pole occupancy angle θ1 is approximately 170°. In therange of the magnetic pole occupancy angle θ1 between 210° and 270°, thetorque ripple is reduced to the minimum 40% when the magnetic poleoccupancy angle θ1 is between 250° and 270°. That is, the ranges inwhich the magnetic pole occupancy angle θ1 of each magnet 23 is150°≦θ1<180° or 210°≦θ1≦270° are preferable ranges in which the torqueripple can be reduced. Further, the range in which the magnetic poleoccupancy angle θ1 is 250°≦θ1 270° is a more preferable range in whichthe torque ripple can be reduced to approximately 40%.

FIG. 2B shows the average torque ratio when the magnetic pole occupancyangle 81 of each magnet 23 is changed. If the average torque when themagnetic pole occupancy angle θ1 is 180° is defined as 100%, the averagetorque is greater than 100% when the magnetic pole occupancy angle θ1 isgreater than 180° and less than or equal to 270°. When the magnetic poleoccupancy angle θ1 is approximately 230°, the average torque isincreased to the maximum value, which is approximately 107% Based on thedata of FIGS. 2A and 2B, the range in which the magnetic pole occupancyangle θ1 of the magnets 23 is 210°≦θ1≦270° is considered to be favorablesince the torque ripple is reduced while improving the average torque.

In the rotor 3 of the present embodiment, the magnetic pole occupancyangle θ1 of the magnets 23 is set to a value within the range of250°≦θ1≦270°, which is within the range of 210°≦θ1≦270°. This increasesthe average torque and reduces the torque ripple (torque pulsation),thereby improving the rotational performance of the rotor 3.

The outside surfaces 24 a and 23 a of the salient poles 24 and themagnets 23 of the rotor 3 are arranged such that the outside surfaces 24a of the salient poles 24 are radially inward relative to the outsidesurfaces 23 a of the magnets 23. That is, in a second gap G2 between thestator 2 (the distal ends 12 a of the teeth 12) and the rotor 3, a gapdistance B corresponding to the salient pole 24 (the shortest gapdistance at the circumferential center) is set to be greater than a gapdistance A corresponding to the magnet 23 (the shortest gap distanceconstant at any circumferential position, that is, constant in thecircumferential direction).

FIGS. 3A, 3B and 3C show the maximum torque ratio, the torque rippleratio, and the radial pulsation ratio when the ratio B/A of the gapdistances B, A is changed, respectively. The torque ripple and theradial pulsation are factors that increase vibrations caused when therotor 3 rotates.

FIG. 3B shows the torque ripple when B/A is changed. The torque ripplewhen B/A=1, that is, when the gap distance A and the gap distance B areequal to each other, is defined as 100 %. As B/A is increased from one,that is, as the salient pole 24 is moved radially inward compared to themagnet 23, the torque ripple is reduced from 100 %. When B/A is in therange from 1 to approximately 1.5, the torque ripple is reducedsubstantially at a constant rate. When B/A is in the range fromapproximately 1.5 to 1.7, the torque ripple continues being reducedalthough the reduction rate is less than the range from 1 toapproximately 1.5. Specifically, the torque ripple is reduced so as tobe approximately 99 % when B/A=1.2, approximately 98.2 % when B/A=1.4,and approximately 97.5 % when B/A=1.6. That is, if 1<B/A, the torqueripple is expected to be reduced.

FIG. 3C shows the radial pulsation ratio when B/A is changed. As in theabove case, the radial pulsation when B/A=1 is defined as 100%. As B/Ais increased from one, the radial pulsation is reduced from 100%substantially at a constant rate. Specifically, the radial pulsation isreduced so as to be approximately 89% when B/A=1.2, approximately 80%when B/A=1.4, and approximately 72% when B/A=1.6. That is, if 1<B/A, theradial pulsation is expected to be reduced.

FIG. 3A shows the maximum torque ratio when B/A is changed. As in theabove cases, the maximum torque ratio when B/A=1 is defined as 100%. AsB/A is increased from 1, the maximum torque is reduced from 100%. In therange in which 1<B/A≦1.6, the maximum torque is reduced substantially ata constant rate. When B/A=1.6, the maximum torque is approximately 92%.When B/A exceeds 1.6, the reduction rate of the maximum torque isgreater than that in the range of 1<B/A≦1.6. That is, the range of1<B/A≦1.6 is a preferable range in which the reduction rate of themaximum torque is relatively small, and the reduction of the maximumtorque is suppressed to or below 10%.

Taking the above factors into consideration, the ratio B/A between thegap distance B of each salient pole 24 relative to the stator 2 and thegap distance A of each magnet 23 is set to a value in the range of1<B/A≦1.6 in the rotor 3 of the present embodiment. Accordingly, whileminimizing the reduction in the maximum torque, it is possible to reducethe torque ripple (FIG. 3B) and the radial pulsation (FIG. 3C), whichlead to vibrations during rotation of the rotor 3.

As described above, factors of vibrations during rotation of the rotor 3are reduced, so that the rotational performance of the rotor 3 isimproved.

The present embodiment provides the following advantages.

(1) In the present embodiment, the opening angle Ykθ of each salientpole 24 opposed to the distal ends 12 a of teeth 12 is greater than orequal to twice the opening angle Tθ of the distal end 12 a of each tooth12. Therefore, the magnetic flux of each salient pole 24 is allowed tosmoothly flow in the radial direction under the influence of two or morethe teeth 12 that are opposed to the salient pole 24. As a result, themagnetic balance of the rotor 3 is improved, and the rotationalperformance is improved. Specifically, the torque is improved and thevibration is reduced.

(2) The motor 1 of the present embodiment has the rotor 3 of aconsequent-pole structure, which includes the salient poles 24integrally formed with the rotor core 22. Each salient pole 24 islocated at the outer circumference of the rotor core 22 and between anadjacent pair of the magnets 23. The salient poles 24 function asmagnetic poles. The stator 2 has slots ST that extends through thestator 2 along the axial direction. Each slot ST is formed between eachan pair of the teeth 12. The segment conductors 14, which have the slotinsertion portions 14 a arranged in the slots ST, correspond to eachphase, and are electrically connected to each other by welding the endsof the slot insertion portions 14 a protruding from the slots ST, sothat the segment coils 13 of multiphase are formed. Compared to coilsformed by winding a continuous lead about teeth as in the conventionalart, the segment coils 13 have a higher space factor in the slot ST, andthe output power of the motor 1 is increased. Accordingly, since therotor 3 is a consequent pole type, the number of the magnets 23 can bekept low. The motor 1 is therefore advantageous in terms of the naturalresource and cost saving. Further, the use of the segment coils 13 ascoils of the stator 2 allows the motor 1 to generate high output power.

(3) The magnetic pole occupancy angle θ1 of each magnet 23 and themagnetic pole occupancy angle θ2 of each salient pole 24 are determinedwith reference to the circumferential midpoint of the first gap G1between a magnet 23 and a circumferentially adjacent salient pole 24(θ1+θ2=360°). The magnetic pole occupancy angle θ1 of each magnet 23 isset to a value in the range of 210°≦θ1≦270°. Therefore, compared to acase in which θ1=180°, that is, a common structure is employed in whichthe magnetic pole occupancy angles θ1 and θ2 of each magnet 23 and eachsalient pole 24 are structurally the same, the torque ripple can bereduced while increasing the average toque (see FIGS. 2A and 2B). Thisimproves the rotational performance of the rotor 3.

If the magnetic pole occupancy angle θ1 is set to any value in the rangeof 150°≦θ1<180°, the torque ripple is reduced compared to a case wherethe magnetic pole occupancy angle θ1 is set to 180° (see FIG. 2A), andthe rotation performance of the rotor 3 is improved.

(4) In the second gap G2 between the stator 2 and the rotor 3 of thepresent embodiment, the ratio B/A between the shortest gap distance A,which corresponds to the magnets 23, and the shortest gap distance B,which corresponds to the salient poles 24 is set to an appropriate valuethat satisfies 1<B/A. This reduces the torque ripple and the radialpulsation, which are causes of vibration when the rotor 3 rotates (seeFIGS. 3B and 3C), thereby improving the rotational performance of therotor 3.

(5) In the present embodiment, the ratio B/A between the shortest gapdistance A, which corresponds to each magnet 23, and the shortest gapdistance B, which corresponds to each salient pole 24, is set to a valuewithin the range of 1<B/A≦1.6. This reduces the torque ripple and theradial pulsation, which are causes of vibration when the rotor 3 rotates(see FIGS. 3A to 3C), while minimizing reduction in the torque, therebyimproving the rotational performance of the rotor 3.

(6) In the present embodiment, the number of the magnets 23 and thenumber of the salient poles 24 are both an odd number, and each magnet23 is at a position opposite to, or 180° away from, one of the salientpoles 24. That is, in a configuration in which each magnet 23 is at aposition opposite to, or 180° away from, one of the salient poles 24,magnetic imbalance is likely to occur and the vibration during rotationof the rotor 3 is likely to increase. Thus, the optimization of theoccupancy angles of the salient poles 24 and the magnets 23 and theoptimization of the ratio B/A of the gap distances are effective inreducing the vibration during rotation of the rotor 3.

The above described first embodiment may be modified as follows.

The shape of the stator 2 of the above described first embodiment may bechanged as necessary. For example, in a modification shown in FIGS. 4,5A, and 5B, a continuous portion 31 and a gap 32 are formed between thedistal ends 12 a of each circumferentially adjacent pair of the teeth 12in the stator core 4. More specifically, as shown in FIGS. 5A and 5B,the stator core 4 is formed by laminating a plurality of laminationmembers E in the axial direction. That is, each lamination member Eincludes a part that is laminated to form the cylindrical portion 11 anda part that is laminated to form the teeth 12 (hereinafter, referred toas the teeth 12 of the lamination member E). To facilitate theillustration, only four of the lamination members E are shown in FIGS.4, 5A and 5B.

In each lamination member E, a continuous portion 31 is formed betweenthe distal ends 12 a of each circumferentially adjacent tooth 12 toconnect the teeth 12 together. A recess 33 is formed by pressing bothsides of each continuous portion 31 of each lamination member E. Thatis, each continuous portion 31 of the lamination members E has athickness in the axial direction that is smaller than the thickness ofthe teeth 12 in the axial direction by the amount of the recesses 33.When the lamination members E are laminated in the axial direction, thecontinuous portions 31 and the gap 32 are alternately formed along theaxial direction between the distal ends 12 a of the teeth 12.

FIGS. 6A and 6B show graphs showing the cogging torque and the averagetorque in the motor having the stator shown in FIGS. 4, 5A and 5B, amotor 1 that does not have the continuous portions 31 as in the stator 2of the previous embodiment (a motor indicated by “open teeth” in FIGS.6A and 6B), and a motor 1 having a stator with no gaps 32. In FIGS. 6Aand 6B, the cogging torque and the average torque of the motor 1 havingno continuous portions 31 are defined as 100%.

As shown in FIG. 6A, the motor 1 of the configuration shown in FIGS. 5Aand 5B reduces the cogging torque to 1 to 5% relative to the motor 1having a stator with no continuous portions 31. The motor 1 having astator without gaps 32 also reduces the cogging torque. As shown in FIG.6B, the average torque of the motor 1 of the present modification isless than that of the motor 1 having a stator without continuous portion31, but 1.5 times greater than that of the motor having a stator withoutgaps.

According to the configuration of the present modification, thecontinuous portions 31 suppress abrupt changes in the magnetic fluxdensity, and as a result, the cogging torque is reduced. Further, whilereducing the cogging torque, the gaps 32 hinder the flow of flux betweenthe distal ends 12 a of the teeth 12. Thus, leakage flux is reduced, sothat the reduction in the torque is suppressed. This improves therotation performance of the rotor 3. Also, the continuous portions 31 atthe distal ends 12 a of the teeth 12 improve the rigidity of the core ofthe stator 2.

In the example shown in FIGS. 5A and 5B, the recesses 33 recessed in theaxial direction by pressing are formed in the continuous portions 31between the distal ends 12 a of the teeth 12 of each lamination memberE. The recesses 33 form the gaps 32. Therefore, the residual stress ofthe pressing performed on the continuous portions 31 of the laminationmember E and the recesses 33 (the gaps 32) formed by the pressinghinders the flow of flux through the distal ends 12 a of the teeth 12.This reduces the leakage flux, and suppresses the reduction in thetorque.

In the example shown in FIGS. 5A and 5B, the gaps 32 are formed byforming the recesses 33 in the continuous portions 31 of the laminationmembers E. However, the gaps 32 may be formed by other methods.

For example, in the example shown in FIGS. 7A to 7D, the stator core 4is formed by alternately laminating first lamination member E1 andsecond lamination member E2 in the axial direction. Each firstlamination member E1 and each second lamination member E2 have partsthat are laminated to form the cylindrical portion 11 and parts that arelaminated to form the teeth 12. In FIGS. 7A and 7B, the cylindricalportion 11 and the teeth 12 of the first and second lamination membersE1, E2 have the same reference numerals as those formed by lamination.To facilitate the illustration, only two of the first and secondlamination members E1, E2 are shown in FIGS. 7C and 7D.

As shown in FIG. 7A, a gap 42 is formed between the distal ends 12 a ofeach adjacent pair of teeth 12 of the first lamination member E1. Incontrast, as shown in FIG. 7B, a continuous portion 41 is formed betweenthe distal ends 12 a of each adjacent pair of the teeth 12 of the secondlamination member E2. Each continuous portion 41 connects adjacent pairof the teeth 12. When the first lamination members E1 and the secondlamination members E2 are laminated in the axial direction, thecontinuous portions 41 and the gaps 42 are alternately formed along theaxial direction between the distal ends 12 a of the teeth 12.

This configuration provides substantially the same advantages as theexample shown in FIGS. 5A and 5B. In addition, in the example shown inFIGS. 7A to 7D, the first lamination members E1 and the secondlamination members E2 are alternately laminated in the axial direction,the inter-teeth continuous portions 41 and the gaps 42 are easily formedbetween the distal ends 12 a of each adjacent pair of the teeth 12.

Further, in the example shown in FIGS. 8A, 8B, and 8C, the stator core 4is formed by laminating a plurality of lamination members E3 in theaxial direction. That is, each lamination member E3 includes a part thatis laminated to form the cylindrical portion 11 and a part that islaminated to form the teeth 12. In FIG. 8A, the cylindrical portion 11and the teeth 12 of the lamination members E3 have the same referencenumerals as those formed by lamination. To facilitate the illustration,only five of the lamination members E3 are shown in FIGS. 8B and 8C.

As shown in FIG. 8A, continuous portions 51 and gaps 52 are alternatelyformed along the circumferential direction between the distal ends 12 aof the teeth 12 of the third lamination member E3. The laminationmembers E3 are laminated such that the continuous portions 51 and thegaps 52 are alternately arranged in the axial direction. In other words,the lamination members E3 that are adjacent to each other in the axialdirection are laminated while being displaced in the circumferentialdirection by the amount of a single tooth 12. Accordingly, thecontinuous portions 51 and the gaps 52 are alternately arranged in theaxial direction between the distal ends 12 a of adjacent teeth 12.

This configuration provides substantially the same advantages as theexample shown in FIGS. 5A and 5B. In addition, in the example shown inFIGS. 8A to 8C, the lamination members E3 having the identical structureare used to form the continuous portions 51 and the gaps 52 between thedistal ends 12 a of the teeth 12. This facilitates the parts control andreduces costs.

The shape of the salient poles 24 of the rotor core 22 of the abovedescribed first embodiment may be changed as necessary.

For example, in the example of FIGS. 9A and 9B, a pair of firstauxiliary grooves 61 is formed in the outside surface 24 a of eachsalient pole 24, which is opposed to teeth 12. The first auxiliarygrooves 61 are at symmetrical positions with respect to thecircumferential center line Q of the salient pole 24. The firstauxiliary grooves 61 have the same shape, and each have a pair of sidesurfaces 61 a, 61 b opposed to each other in the circumferentialdirection. Of the side surfaces of each first auxiliary groove 61, theside surface located inside with respect to the circumferentialdirection (the one closer to the circumferential center line Q) isdefined as the side surface 61 a, and the side surface located outsidewith respect to the circumferential direction (the one closer to acircumferential end of the salient pole 24) is defined as the sidesurface 61 b. The first auxiliary groove 61 extends linearly along theaxial direction.

As shown in FIG. 10, when the opening degree of the salient pole 24about the axis P is defined as Ykθ(°), the opening degree of the distalend 12 a of the tooth 12 about the axis P is defined as Tθ(*), and thenumber of the teeth is represented by L, the positional angle D1 of thefirst auxiliary groove 61 (the angle D1 from the circumferential centerQ of the salient pole 24 to the side surface 61 a of the first auxiliarygroove 61) is determined to satisfy the expressionD1=Tθ+(a−1)×360(°)/L−Ykθ/2 (where a is a natural number). 360(°)/L inthe expression indicates the angle between the circumferential centersof circumferentially adjacent teeth 12 about the axis P. That is, theright side of the expression Tθ+(a−1)×360(°)/L indicates the openingdegree of circumferentially consecutive teeth 12 the number of which isrepresented by a. Therefore, when the configuration satisfies theexpression, the angle from a circumferential end 24 b of the salientpole 24 (left end as viewed in FIG. 10) to the side surface 61 a of afirst auxiliary groove 61 that is farther from the end 24 b, that is,Ykθ/2+D1 is equal to the angle between the circumferential ends ofcircumferentially consecutive teeth 12 the number of which isrepresented by a. FIG. 10 shows a configuration in which a=3.

That is, in this configuration, as shown in FIG. 10, when thecircumferential end 24 b of the salient pole 24 is aligned in the radialdirection with a first end 12 x (left end) of the distal end 12 a of anytooth 12 (a tooth 12 b in FIG. 10), the side surface 61 a of the firstauxiliary groove 61 is aligned in the radial direction with acircumferential second end 12 y (right end) of a tooth 12 that is an athtooth (a tooth 12 c in FIG. 10) from the tooth 12 b along thecircumferential direction (rightward). “Being aligned in the radialdirection” indicates a state in which a circumferential end of thesalient pole 24 and a circumferential end of the tooth 12 b are locatedon the same straight line extending along the radial direction.

FIG. 11 shows the waveform of the cogging torque when the rotor 3 isrotating. The waveform represented by the alternate long-and-shortdashed line in FIG. 11 is the waveform of the main component of thecogging torque (the cogging torque waveform of a configuration in whichno first auxiliary grooves 61 are formed in any salient poles 24), andthe waveform represented by the broken line is the waveform of thecogging torque generated by the first auxiliary grooves 61. The waveformrepresented by the solid line is the waveform of the cogging torquegenerated in the motor 1 of the configuration shown in FIGS. 9 and 10,and is a composite waveform of the main component of the cogging torque(the waveform represented by the alternate long-and-short dashed line)and the cogging torque waveform generated by the first auxiliary grooves61 (the waveform represented by the broken line).

The rotational angle R of the rotor 3 in FIG. 11 is the rotational angleof the rotor 3 in the state shown in FIG. 10. At the rotational angle R,the circumferential end 24 b of the salient pole 24 and thecircumferential first end 12 x of the tooth 12 b are aligned with eachother in the radial direction. Thus, flux tends to be concentrated inradially aligned sections. As a result, the main component of thecogging torque has the negative peak value. At this time, the sidesurface 61 a of the first auxiliary groove 61 and the circumferentialsecond end 12 y of the tooth 12 c are aligned with each other. Thus,flux tends to be concentrated in the radially aligned sections. As aresult, the cogging torque generated by the first auxiliary groove 61has a positive peak value. The peak of the main component of the coggingtorque and the peak of the cogging torque generated by the firstauxiliary groove 61, which appear at the rotation angle R, have oppositephases and substantially the same magnitude. The cogging torquestherefore cancel each other (see the waveform of the solid line in FIG.11). Accordingly, the cogging torque generated when the rotor 3 isrotating is reduced.

According to this configuration, the first auxiliary grooves 61 formedin the outside surface 24 a (surface) of each salient pole 24 that isopposed to some of the teeth 12 optimizes the flow of flux in thesalient pole 24, thereby reducing the cogging torque. Also, since theexpression D1=Tθ+(a−1)×360(°)/L−Ykθ/2 is satisfied, the cogging torquegenerated in the first auxiliary grooves 61 of each salient pole 24serves as a cancelling component that reduces the cogging torquegenerated at the circumferential end 24 b of the salient pole 24. Thecogging torque generated in the entire motor 1 can be reduced, and therotation performance of the rotor 3 is therefore improved. Also, sincethe first auxiliary grooves 61 are formed to correspond to bothcircumferential ends of the salient pole 24, the cogging torque isfurther reduced.

FIG. 12 shows the magnitude of the cogging torque when the grooveopening degree W of the first auxiliary grooves 61 is changed. As shownin FIG. 12, as the groove opening degree W is increased from zerodegrees, the cogging torque decreases. When the groove opening degree Wis approximately 1.2 degrees, the cogging torque is the smallest.

In addition to the configuration shown in FIGS. 9A, 9B and 10, secondauxiliary grooves. 62 shown in FIG. 13 may be provided separately fromthe first auxiliary grooves 61. Like the first auxiliary grooves 61, apair of second auxiliary grooves 62 is formed at symmetrical positionswith respect to the circumferential center line Q of each salient pole24. The second auxiliary grooves 62 have the same shape, and each have apair of side surfaces 62 a, 62 b opposed to each other in thecircumferential direction. Of the side surfaces of each second auxiliarygroove 62, the side surface located inside with respect to thecircumferential direction (the one closer to the circumferential centerline Q) is defined as the side surface 62 a, and the side surfacelocated outside with respect to the circumferential direction (the onecloser to a circumferential end of the salient pole 24) is defined asthe side surface 62 b. The second auxiliary groove 62 extends linearlyalong the axial direction.

The positional angle D2 of each second auxiliary groove 62 (the angle D2from the circumferential center Q of the salient pole 24 to the sidesurface 62 a of the second auxiliary groove 62) is determined to satisfythe expression D2=D1+360(°). Accordingly, the positional angle D2 of thesecond auxiliary grooves 62 is determined such that the angle from thecircumferential end 24 b of the salient pole 24 to the side surface 62 aof a second auxiliary groove 62 that is farther from the end 24 b (thatis, Ykθ/2+D1) is equal to the angle between the circumferential ends ofcircumferentially consecutive teeth 12 the number of which isrepresented by a+1. FIG. 13 shows a configuration in which a=3.

That is, in this configuration, when the circumferential end 24 b ofeach salient pole 24 is aligned in the radial direction with the firstend 12 x of the distal end 12 a of any tooth 12 b, the side surface 61 aof the first auxiliary groove 61 is aligned in the radial direction witha circumferential second end 12 y of a tooth 12 c that is an ath toothfrom the tooth 12 b along the circumferential direction (rightward).Also, the side surface 62 a of the second auxiliary groove 62 is alignedin the radial direction with a circumferential second end 12 z of atooth 12 d that is an (a+1)th tooth from the tooth 12 b along thecircumferential direction (rightward).

According to this configuration, not only the cogging torque generatedin the first auxiliary grooves 61, but also the cogging torque generatedin the second auxiliary grooves 62 serves as a cancelling component thatreduces the cogging torque generated at the circumferential end 24 b ofthe salient pole 24. The cogging torque generated in the entire motor 1is therefore further reduced.

In the first embodiment, the number of the magnets 23 and the number ofthe salient poles 24 are five each, so that the rotor 3 has ten magneticpoles. However, other configurations may be employed. That is, thenumber of the magnets 23 and the number of the salient poles 24 may bechanged as necessary.

In the first embodiment, the shapes of the outside surfaces 23 a and 24a of the magnets 23 and the salient poles 24 may be changed asnecessary. In the first embodiment, the outside surfaces 23 a of themagnets 23 are arcuate and arranged on the same circle, and the outsidesurface 24 a of each salient pole 24 has a greater curvature than thatof the outside surface 23 a. Also, the outside surfaces 23 a, 24 a maybe curved and located on the same circle. Further, the outside surfaces23 a, 24 a may be curved to have a large curvature. The curvature of theoutside surfaces 23 a, 24 a does not need to be constant, but may bechanged along the circumferential direction or changed linearly. Otherthan these modifications, the shape of the magnets 23 and the shape ofthe rotor core 22 including the salient poles 24 may be changed asnecessarily.

A second embodiment of the present invention will now be described withreference to the drawings.

As shown in FIG. 14A, an inner rotor type motor 201 of the presentembodiment includes a substantially annular stator 202 and a rotor 203arranged radially inward of the stator 202.

The stator 202 includes a stator core 204. The stator core 204 has acylindrical portion 211 and a plurality of teeth 212, the number ofwhich is twelve in the present embodiment. The teeth 212 are arrangedalong the circumferential direction on the inner circumferential surfaceof the cylindrical portion 211. The teeth 212 extend radially inwardfrom the inner circumferential surface of the cylindrical portion 211.The teeth 212 are formed at equal angular intervals in thecircumferential direction. Coils 213 of the U-phase, V-phase, andW-phase are sequentially wound about the teeth 212 by concentratedwinding. Each tooth 212 has at its distal end a pair of protrudingportions 212 a protruding in the circumferential direction. The surface212 b (the inside surface in the radial direction) of each tooth 212 isformed to be arcuate the center of which coincides with the axis P ofthe motor 201. The surface 212 b of each tooth 212 is formed from one ofthe protruding portion 212 a to the other protruding portion 212 a. Thetooth 212 is formed to be symmetrical with respect to the center line inthe circumferential direction.

The rotor 203 includes a substantially annular rotor core 222, aplurality of (four in the present embodiment) magnets 223, and salientpoles 224. The rotor core 222 is made of magnetic metal and adhered tothe outer circumferential surface of a rotary shaft 221. The magnets 223are arranged on the outer circumferential surface of the rotor core 222along the circumferential direction. Each salient pole 224 is located inthe outer circumferential portion of the rotor core 222 and between acircumferentially adjacent pair of the magnets 223. The magnets 223function as north poles. The salient poles 224 are integrally formedwith the rotor core 222. That is, the magnets 223 and the salient poles224 are alternately arranged on the outer circumferential portion of therotor 203 in the circumferential direction at equal angular intervals.The rotor 203 is a consequent pole type with eight magnetic poles thatcauses the salient poles 224 to function as south poles in relation tothe north pole magnets 223. The number of the magnetic poles (eightmagnetic poles) of the rotor 203 is ⅔ of the number (twelve) of theteeth 212, and the ratio of the number of the magnetic poles of therotor 203 and the number of the teeth 212 is 2:3.

The outside surface 223 a of each magnet 223 has an arcuate shape thecenter of which coincides with the axis P, and is opposed to the surface212 b of the corresponding tooth 212 in the radial direction. Thecircumferential length of each magnet 223 is slightly greater than thatof each salient pole 224. The inside surface 223 b of each magnet 223 isfixed to a fixing surface 225 provided between a circumferentiallyadjacent pair of the salient poles 224 in the rotor core 222. A gapexists between each magnet 223 and a circumferentially adjacent salientpole 224. The magnets 223 are configured such that the outside surfaces223 a are located on the same circumference.

Each salient pole 224 has a sectoral cross section in the axialdirection, and has an outside surface 224 a (outside surface in theradial direction) that bulges outward in the radial direction. A pair ofauxiliary grooves 231, 232 (both are first auxiliary grooves) is formedin the outside surface 224 a of each salient pole 224. The auxiliarygrooves 231, 232 are at symmetrical positions with respect to thecircumferential center line S of the salient pole 240. The auxiliarygrooves 231, 232 have the same shape, and have a pair of side surfaces231 a, 231 b and a pair of side surfaces 232 a, 232 b opposed to eachother in the circumferential direction, respectively. The side surfacesof the auxiliary grooves 231, 232 located inside with respect to thecircumferential direction (the ones closer to the circumferential centerline S) are defined as the side surfaces 231 a, 232 a, and the sidesurfaces located outside with respect to the circumferential direction(the ones closer to the circumferential ends of the salient pole 224)are defined as the side surfaces 231 b, 232 b.

The auxiliary grooves 231, 232 extend linearly along the axialdirection. The depth of the auxiliary grooves 231, 232 is set to be ⅓ ofthe radial dimension of the salient poles 224. As described above, theauxiliary grooves 231, 232 are at symmetrical positions with respect tothe circumferential center line S of the salient pole 224. Thus, theangle from the circumferential center line S to the inner side surface231 a of the auxiliary groove 231 about the axis P and the angle fromthe circumferential center line S to the inner side surface 232 a of theauxiliary groove 232 about the axis P are equal to each other.Hereinafter, this angle is referred to as a positional angle KC1 of theauxiliary grooves 231, 232 (see FIG. 14B).

As shown in FIG. 15A, the opening angle KA between circumferential ends212 c and 212 d of the surface 212 b of each tooth 212 about the axis Pis set to be smaller than the opening angle KB between circumferentialends 224 b and 224 c of each salient pole 224 about the axis P. Thepositional angle KC1 of the auxiliary grooves 231, 232 is set to satisfythe expression KC1=KA−KB/2. Accordingly, in a state where a tooth 212 isopposed to a salient pole 224 in the radial direction as shown in FIG.15A, when the circumferential first end 212 c of the surface 212 b ofthe tooth 212 is aligned in the radial direction with thecircumferential first end 224 b of the salient pole 224 (specifically, apart at which the circumferential side surface of the salient pole 224and the outside surface 224 a in the radial direction intersect), thecircumferential second end 212 d of the surface 212 b of the tooth 212is aligned in the radial direction with the side surface 231 a of theauxiliary groove 231 (specifically, a part at which the side surface 231a and the outer side surface 240 a,of the salient pole 224 intersect).Likewise, when the circumferential second end 212 d of the surface 212 bof the tooth 212 is aligned in the radial direction with thecircumferential second end 224 c of the salient pole 224 as shown inFIG. 15B, the circumferential first end 212 c of the surface 212 b ofthe tooth 212 is aligned in the radial direction with the side surface232 a of the auxiliary groove 232. “Being aligned in the radialdirection” indicates a state in which the circumferential ends 224 b,224 c of the salient pole 224 and the circumferential ends 212 c, 212 dof the tooth 212 are located on the same straight line extending alongthe radial direction.

FIG. 16 shows the waveform of the cogging torque when the rotor 203 isrotating. The waveform represented by the alternate long-and-two-shortdashed line in FIG. 16 is the waveform of the main component of thecogging torque, and is the same as the waveform of the cogging torque ina rotor having no auxiliary grooves 231, 232 in the salient poles 224.The waveform represented by an alternate long-and-short dashed line isthe waveform of the cogging torque generated by the auxiliary grooves231, 232. The waveform represented by the solid line is the waveform ofthe cogging torque generated in the motor 201 of the present embodiment,and is a composite waveform of the main component of the cogging torque(the waveform represented by the alternate long-and-two-short dashedline) and the cogging torque waveform generated by the first auxiliarygrooves 231, 232 (the waveform represented by the alternatelong-and-short dashed line).

FIG. 16 shows the cogging torque generated at the rotational angle R1 ofthe rotor 203 shown in FIG. 15A, that is, when the circumferential firstend 224 b of each salient pole 224 is aligned in the radial directionwith the circumferential first end 212 c of the corresponding tooth 212.At the rotation angle R1, the circumferential first end 224 b of eachsalient pole 224 and the circumferential first end 212 c of thecorresponding tooth 212 are aligned with each other in the radialdirection. Thus, magnetic flux is likely to be concentrated in a partclose to the circumferential first end 212 c of the tooth 212. As aresult, the main component of the cogging torque is increased, the maincomponent of the cogging torque (the waveform represented by thealternate long-and-two-short dashed line).

In the motor 201 of the present embodiment, the positional angle KC1 ofthe auxiliary grooves 231, 232 is set to satisfy the expressionKC1=KA−KB/2. Thus, the circumferential second end 212 d of each tooth212 is aligned in the radial direction with the side surface 231 a ofthe auxiliary groove 231 at the rotational angle R1. Therefore, the fluxat the time is easily dispersed in the vicinity of the circumferentialsecond end 212 d of each tooth 212, and is less likely to beconcentrated in the vicinity of the circumferential first end 212 c ofthe tooth 212. As shown in FIG. 16, the cogging torque generated by theauxiliary grooves 231, 232 has at the rotational angle R1 a peak of theopposite phase (positive) to the cogging torque, and therefore serves asa component cancelling the main component of the cogging torque. Thepeak is generated by the auxiliary groove 231. Therefore, the coggingtorque of the entire motor 201 (the waveform indicated by solid line),which is the composite of the main component of the cogging torque andthe cogging torque generated by the auxiliary grooves 231, 232, has awaveform in which the peak of the main component of the cogging torqueat the rotational angle R1 is reduced. As described above, the coggingtorque generated can be reduced by the auxiliary groove 231, and therotation performance of the rotor 3 is improved. The absolute value ofthe peak of the cogging torque generated by the auxiliary grooves 231,232 is less than the absolute value of the peak of the main component ofthe cogging torque.

The other auxiliary groove 232 operates in the same manner as theauxiliary groove 231. Specifically, in a state where each salient pole224 is opposed to a tooth 212 as shown in FIG. 15B, when thecircumferential second end 224 c of the salient pole 224 is aligned inthe radial direction with the circumferential second end 212 d of thetooth 212 (the rotational angle R2 in FIG. 15B), the circumferentialfirst end 212 c of the tooth 212 is aligned in the radial direction withthe side surface 232 a of the auxiliary groove 232. Thus, as in the caseof the auxiliary groove 231 described above, the cogging torquegenerated by the auxiliary grooves 231, 232 functions as a componentcancelling the peak of the opposite phase of the main component of thecogging torque at the rotational angle R2, that is, the main componentof the cogging torque. This further reduces the cogging torque, and therotation performance of the rotor 203 is improved.

The graph of the solid line in FIG. 17 shows the cogging torque ratiowhen the ratio W1/T is changed, in which W1 represents thecircumferential width of the auxiliary grooves 231, 232 (see FIG. 15B)with reference to the side surfaces 231 a, 232 a located inside of theauxiliary grooves 231, 232 (closer to the circumferential center lineS), and T represents the circumferential interval T between the distalends of adjacent teeth 212 (see FIG. 15B), or between the protrudingportions 212 a. In FIG. 17, if the cogging torque when W1/T=0, that is,when there are no auxiliary grooves 231, 232, is defined as 1, thecogging torque decreases from W1/T=0 to W1/T=2.5. The cogging torque hasthe minimum value of 0.5 when W1/T=2.5. In the range from W1/T=2.5 toW1/T=3.5, the cogging torque increases from the minimum value, butremains less than 1. That is, the cogging torque is less than 1 in therange of 0<W1/T<3.5. Thus, if W1/T is set to a value in this range, thecogging torque is expected to become lower than that in the case whereno auxiliary grooves 231, 232 are formed. If W1/T=2.5, the coggingtorque is reduced to the half. That is, the cogging torque is mostsignificantly reduced.

The present embodiment provides the following advantages.

(7) In the present embodiment, the auxiliary grooves 231, 232 are formedin the outside surface 224 a of each salient pole 224 of the rotor 203,and the positional angle KC1 the auxiliary grooves 231, 232 satisfiesthe expression KC1=KA−KB/2. Therefore, when each tooth 212 is opposed toa salient pole 224 in the radial direction, and the circumferentialfirst end 212 c of the surface 212 b of the tooth 212 is aligned in theradial direction with the circumferential first end 224 b of the salientpole 224 while the rotor 203 is rotating, the circumferential second end212 d of the tooth 212 is aligned in the radial direction with the sidesurface 231 a of the auxiliary groove 231. Also, when each tooth 212 isopposed to a salient pole 224 in the radial direction, and thecircumferential second end 212 d of the surface 212 b of the tooth 212is aligned in the radial direction with the circumferential second end224 c of the salient pole 224 while the rotor 203 is rotating, thecircumferential first end 212 c of the tooth 212 is aligned in theradial direction with the side surface 232 a of the auxiliary groove232. At this time the cogging torque generated in the vicinity of thecircumferential first and second ends 212 c, 212 d of the tooth 212 thatare aligned with the side surfaces 231 a, 232 a of the auxiliary grooves231, 232 (the cogging torque generated by the auxiliary grooves 231,232) serves as a component cancelling the cogging torque (maincomponent) generated in the vicinity of the circumferential ends 212 c,212 d of the tooth 212 that is aligned in the radial direction with thecircumferential first and second ends 224 b, 224 c of the salient pole224. Thus, it is possible to reduce the cogging torque generated by theentire motor 201, so as to improve the rotation performance of the rotor203.

(8) In the present embodiment, the auxiliary grooves 231, 232 are formedin a pair along the circumferential direction to be symmetrical withrespect to the circumferential center line S in each salient pole 224.Since the auxiliary grooves 231, 232 are formed in a pair to correspondto the circumferential first and second ends 224 b, 224 c of eachsalient pole 224, respectively, the cogging torque is further reduced.

(9) In the present embodiment, the ratio W1/T between thecircumferential width W1 of the auxiliary grooves 231, 232 and theinterval T between circumferentially adjacent teeth 212 is set tosatisfy the expression 0<W1/T<3.5. This enables further reduction in thecogging torque (see FIG. 4), and improves the rotation performance ofthe rotor 203.

A third embodiment of the present invention will now be described withreference to the drawings.

As shown in FIGS. 18A and 18B, in addition to the configuration of thesecond embodiment, a motor 301 of the present embodiment has insideauxiliary grooves 331, 332, which serve as second auxiliary grooves andare formed in the outside surface 224 a of each salient pole 224. Likeor the same reference numerals are given to those components that arelike or the same as the corresponding components of the secondembodiment, and the detailed description thereof will be omitted.

The inside auxiliary grooves 341, 342 are formed at positions locatedinside with respect to the circumferential direction of the auxiliarygrooves 231, 232 (first auxiliary grooves), and symmetrical with respectto the circumferential center line S of the salient pole 224. The insideauxiliary grooves 341, 342 have the same shape, and have a pair of sidesurfaces 341 a, 341 b and a pair of side surfaces 342 a, 342 b opposedto each other in the circumferential direction, respectively. The sidesurfaces located inside (the ones closer to the circumferential centerline S) are defined as first side surfaces 341 a, 342 a, and the sidesurfaces located outside (the ones closer to the circumferential ends ofthe salient pole 224) are defined as second side surfaces 341 b, 342 b.

Like the outside auxiliary grooves 231, 232, the inside auxiliarygrooves 341, 342 extend linearly along the axial direction. The depth(the dimension in the radial direction) of the inside auxiliary grooves341, 342 is set to be substantially equal to the depth of the auxiliarygrooves 231, 232 and ⅓ of the radial dimension of the salient poles 224.As described above, the inside auxiliary grooves 341, 342 are atsymmetrical positions with respect to the circumferential center line Sof the salient pole 224. Thus, the angle from the circumferential centerline S to the outer side surface 341 b of the inside auxiliary groove341 about the axis P and the angle from the circumferential center lineS to the outer side surface 342 b of the inside auxiliary groove 342about the axis P are equal to each other. Hereinafter, this angle isreferred to as a positional angle KC2 of the inside auxiliary grooves341, 342 (see FIG. 18B).

If the opening angle between a magnet 223 and a salient pole 224 aboutthe axis P is indicated by KD, the positional angle KC2 of the insideauxiliary grooves 341, 342 is set to satisfy the expressionKC2=KA−KB/2−KD. As in the second embodiment, KA and KB are defined asthe opening degree of the surface 212 b of each tooth 212 and theopening degree of each salient pole 224, respectively (see FIG. 15A).Accordingly, as shown in FIG. 19A, when the circumferential first end212 c of the surface 212 b of a tooth 212 is aligned in the radialdirection with the circumferential first end 323 b of the magnet 223adjacent to the opposed salient pole 224 (specifically, a part at whichthe circumferential side surface of the magnet 223 and the outsidesurface 323 a in the radial direction intersect), the circumferentialsecond end 212 d of the tooth 212 is aligned in the radial directionwith the outer side surface 341 b of the inside auxiliary groove 341(specifically, a part at which the side surface 341 b and the outsidesurface 224 a of the salient pole 224 intersect). Likewise, when thecircumferential second end 212 d of the tooth 1 is aligned in the radialdirection with the circumferential first end 323 c of the magnet 223adjacent to the opposed salient pole 224 (the bottom right magnet 223 inFIG. 19A) as shown in FIG. 19D, the circumferential first end 212 c ofthe surface 212 b of the tooth 212 is aligned in the radial directionwith the outer side surface 342 b of the inside auxiliary groove 342.

FIG. 20 shows the waveform of the cogging torque when the rotor 303 ofthe present embodiment is rotating. The waveform represented by thealternate long-and-two-short dashed line in FIG. 20 is the waveform ofthe main component of the cogging torque, and is the same as thewaveform of the cogging torque in a rotor having neither auxiliarygrooves 231, 232 nor inside auxiliary grooves 341, 342 in the salientpoles 224. The waveform represented by the alternate long-and-shortdashed line is the waveform of the cogging torque generated by theauxiliary grooves 231, 232 and the inside auxiliary grooves 341, 342.The waveform represented by the solid line is the waveform of thecogging torque generated in the motor 301 of the present embodiment, andis a composite waveform of the main component of the cogging torque (thewaveform represented by the alternate long-and-two-short dashed line)and the cogging torque waveform generated by the first auxiliary grooves231, 232 and the inside auxiliary grooves 341, 341 (the waveformrepresented by the alternate long-and-short dashed line).

The rotational angle of the rotor 303 shown in FIG. 19, that is, therotational angle when the circumferential first end 212 c of a tooth 212is aligned with the circumferential first end 323 b of a magnet 223adjacent to the opposed salient pole 224 is defined as R3. At this time,at least a part of the tooth 212 is moved to a non-opposed state fromthe state opposed to the magnet 223 in the radial direction. Thus,magnetic flux is likely to be concentrated in a part close to thecircumferential first end 212 c of the tooth 212. As a result, the maincomponent of the cogging torque is increased.

In the motor 301 of the present embodiment, the positional angle KC2 ofthe inside auxiliary grooves 341, 342 is set to satisfy the expressionKC2=KA−KB/2. Thus, the circumferential second end 212 d of the tooth 212is aligned in the radial direction with the outer side surface 341 b ofthe inside auxiliary groove 341 at the rotational angle R3. Therefore,the flux at the time is easily dispersed to the circumferential secondend 212 d of each tooth 212, and is less likely to be concentrated inthe vicinity of the circumferential first end 212 c of the tooth 212. Asshown in FIG. 20, the cogging torque generated by the auxiliary grooves231, 232 and the inside auxiliary grooves 341, 342 has at the rotationalangle R3 a component of the opposite phase (positive) to the coggingtorque, that is, a component cancelling the main component of thecogging torque. The cancelling component is generated by the insideauxiliary groove 341. Therefore, the cogging torque of the entire motor301 (the waveform indicated by the solid line) has a waveform in whichthe peak of the main component of the cogging torque at the rotationalangle R3 is reduced. As described above, the cogging torque generatedcan be reduced by the inside auxiliary groove 341, and the rotationperformance of the rotor 303 is improved.

The other inside auxiliary groove 342 operates in the same manner as theinside auxiliary groove 341. Specifically, when the circumferentialsecond end 212 d of the tooth 212 is aligned in the radial directionwith the circumferential first end 323 c of the magnet 223 adjacent tothe opposed salient pole 224 as shown in FIG. 19D (at the rotationalangle R4 in FIG. 20), the circumferential first end 212 c of the tooth212 is aligned in the radial direction with the outer side surface 342 bof the inside auxiliary groove 342. Thus, as in the case of the insideauxiliary groove 341 described above, the cogging torque generated bythe auxiliary grooves 231, 232 and the inside auxiliary grooves 341, 342functions as a component cancelling the component of the opposite phaseof the main component of the cogging torque at the rotational angle R4,that is, the main component of the cogging torque. This further reducesthe cogging torque, and the rotation performance of the rotor 303 isimproved.

Also, since the auxiliary grooves 231, 232 are provided in addition tothe inside auxiliary grooves 341, 342 in the present embodiment, thecogging torque is reduced also at the rotational angles R1 and R2 asdescribed in the second embodiment (refer to FIGS. 19B, 19C, and 20).

The graph of the alternate long-and-short dashed line in FIG. 17 showsthe cogging torque ratio when the ratio W2/T is changed, in which W2represents the circumferential width of the inside auxiliary grooves341, 342 (see FIG. 18B) with reference to the outer side surfaces 341 b,342 b located outside of the inside auxiliary grooves 341, 342, andrepresents the circumferential interval T between the distal ends ofadjacent teeth 212 (see FIG. 18B), or between the protruding portions212 a. In FIG. 17, the cogging torque when W2/T=0, that is, the coggingtorque in a configuration without the inside auxiliary grooves 341, 342,is defined as 1. As shown in FIG. 17, the cogging torque decreases fromW2/T=0 to W2/T=0.6. The cogging torque has the minimum value of 0.7 whenW2/T=0.6. In the range from W2/T=0.6 to W2/T=1.2, the cogging torqueincreases from the minimum value, but remains less than 1. That is, thecogging torque is less than 1 in the range of 0<W2/T<1.2. Thus, if W2/Tis set to a value in this range, the cogging torque is expected to belower than that in the case where no inside auxiliary grooves 341, 342are formed. If W2/T=0.6, the cogging torque is reduced to approximately70%. That is, the cogging torque is most significantly reduced.

The present embodiment provides the following advantages.

(10) In the present embodiment, the inside auxiliary grooves 341, 342are formed in the outside surface 224 a of each salient pole 224 of therotor 303, and the positional angle KC2 satisfies the expressionKC2=KA−KB/2−KD. Therefore, when the circumferential first end 212 c ofthe surface 212 b of each tooth 212 is aligned in the radial directionwith the circumferential first end 323 b of the magnet 223 adjacent tothe opposed salient pole 224 while the rotor 303 is rotating, thecircumferential second end 212 d of the tooth 212 is aligned in theradial direction with the side surface 341 b of the inside auxiliarygroove 341. Also, when the circumferential second end 212 d of thesurface 212 b of a tooth 212 is aligned in the radial direction with thecircumferential first end 323 c of the magnet 223 adjacent to theopposed salient pole 224 while the rotor 303 is rotating, thecircumferential first end 212 c of the tooth 212 is aligned in theradial direction with the side surface 342 b of the inside auxiliarygroove 342. At this time the cogging torque generated in the vicinity ofthe circumferential ends 212 c, 212 d of the tooth 212 that are alignedin the radial direction with the side surfaces 341 b, 342 b of theinside auxiliary grooves 341, 342 (the cogging torque generated by theinside auxiliary grooves 341, 342) serves as a cancelling componentreducing the cogging torque (main component) generated in the vicinityof the circumferential ends 212 c, 212 d of the tooth 212 that isaligned in the radial direction with the circumferential first ends 323b, 323 c of the magnet 223. Thus, it is possible to reduce the coggingtorque generated by the entire motor 301, so as to improve the rotationperformance of the rotor 303.

(11) in the present embodiment, the inside auxiliary grooves 341, 342are formed in a pair along the circumferential direction to besymmetrical with respect to the circumferential center line S in eachsalient pole 224. Since the inside auxiliary grooves 341, 342 are formedin a pair to correspond to the circumferential first ends 323 b, 323 cof the magnets 223 on both sides of the salient pole 224, the coggingtorque is further reduced.

(12) In the present embodiment, the ratio W2/T between thecircumferential width W2 of the inside auxiliary grooves 341, 342 andthe interval T between circumferentially adjacent teeth 212 is set tosatisfy the expression 0<W2/T<1.2. This enables further reduction in thecogging torque (see FIG. 17), and improves the rotation performance ofthe rotor 303.

(13) In the present embodiment, since each salient pole 224 has both ofthe auxiliary grooves 231, 232 serving as the first auxiliary groovesand the inside auxiliary grooves 341, 342 serving as the secondauxiliary grooves, the cogging torque is further reduced.

A fourth embodiment of the present invention will now be described withreference to the drawings.

A motor 401 of the present embodiment is different from the secondembodiment in that auxiliary grooves (tooth auxiliary grooves 451, 452)are formed in each tooth 212, but not in the salient poles 224. Thus,like or the same reference numerals are given to those components thatare like or the same as the corresponding components of the secondembodiment, and the detailed description thereof will be omitted.

As shown in FIGS. 21A and 21B, a pair of tooth auxiliary grooves 451,452 is formed in the surface 212 b of each tooth 212. The toothauxiliary grooves 451, 452 have a pair of side surfaces 451 a, 451 b anda pair of side surfaces 452 a, 452 b opposed to each other in thecircumferential direction, respectively, and extend in the axialdirection. The tooth auxiliary grooves 451, 452 have the same shape, andare formed to be symmetrical with respect to the circumferential centerline H of each tooth 212. The side surfaces located inside (the onescloser to the circumferential center line H) are defined as first sidesurfaces 451 a, 452 a, and the side surfaces located outside (the onescloser to the circumferential ends of the tooth 212) are defined assecond side surfaces 451 b, 452 b.

The tooth auxiliary grooves 451, 452 are formed to be symmetrical withrespect to the circumferential center line H of each tooth 212. Thus,the angle from the circumferential center line H to the outer sidesurface 451 b of the tooth auxiliary groove 451 about the axis P and theangle from the circumferential center line H to the outer side surface452 b of the tooth auxiliary groove 452 about the axis P are equal toeach other. Hereinafter, this angle is referred to as a positional angleKC3 of the tooth auxiliary grooves 451, 452 (see FIG. 21B).

If the angle between the circumferential center lines H of adjacent pairof the teeth 212 is indicated by KE, the positional angle KC3 of thetooth auxiliary grooves 451, 452 is set to satisfy the expressionKC3=KA/2+KE−KB. As in the second embodiment, KA and KB are defined asthe opening degree of the surface 212 b of each tooth 212 and theopening degree of each salient pole 224, respectively (see FIG. 15A).FIG. 22A shows a state in which the circumferential first end 224 b of asalient pole 224 is aligned in the radial direction with thecircumferential first end 212 c of the surface 212 b of the opposedtooth 212. In this state, the circumferential second end 224 c of thesalient pole 224 is aligned in the radial direction with the outer sidesurface 451 b of the tooth auxiliary groove 451 (specifically, a partwhere the side surface 451 b and the surface 212 b of the tooth 212intersect) in the tooth (the tooth 212 e in FIG. 22A) that is adjacentto the tooth 212 that is aligned with the circumferential first end 224b. Likewise, FIG. 22B shows a state in which the circumferential secondend 224 c of a salient pole 224 is aligned in the radial direction withthe circumferential second end 212 d of the opposed tooth 212. In thisstate, the circumferential first end 224 b of the salient pole 224 isaligned in the radial direction with the outer side surface 452 b of thetooth auxiliary groove 452 in the tooth (the tooth 212 f in FIG. 22B)that is adjacent to the tooth 212 that is aligned with thecircumferential second end 224 c.

FIG. 23 shows the waveform of the cogging torque when the rotor 403 ofthe present embodiment is rotating. The waveform represented by analternate long-and-two-short dashed line in FIG. 23 is the waveform ofthe main component of the cogging torque, and is the same as thewaveform of the cogging torque in a rotor having no tooth auxiliarygrooves 451, 452 in the teeth 212. The waveform represented by analternate long-and-short dashed line is the waveform of the coggingtorque generated by the tooth auxiliary grooves 452. The waveformrepresented by the solid line is the waveform of the cogging torquegenerated in the motor 401 of the present embodiment, and is a compositewaveform of the main component of the cogging torque (the waveformrepresented by the alternate long-and-two-short dashed line) and thecogging torque waveform generated by the tooth auxiliary grooves 451,452 (the waveform represented by the alternate long-and-short dashedline).

The rotational angle of the rotor 403 shown in FIG. 22A, that is, therotational angle when the circumferential first end 224 b of eachsalient pole 224 is aligned with the circumferential first end 212 c ofthe opposed tooth 212 is defined as R5. At this time, magnetic flux islikely to be concentrated in a part close to the circumferential firstend 224 b of the salient pole 224. As a result, the main component ofthe cogging torque is increased, and the main component of the coggingtorque has the negative peak value (see FIG. 23).

In the motor 401 of the present embodiment, the positional angle KC3 ofthe tooth auxiliary grooves 451, 452 is set to satisfy the expressionKC3=KA/2+KE−KB. Thus, the circumferential second end 224 c of eachsalient pole 224 is aligned in the radial direction with the outer sidesurface 451 b of the tooth auxiliary groove 451 of the tooth 212 e atthe rotational angle R5. Therefore, the flux is easily dispersed in thevicinity of the circumferential second end 224 c of each salient pole224, and is less likely to be concentrated in the vicinity of thecircumferential first end 224 b of each salient pole 224. As shown inFIG. 23, the cogging torque generated by the tooth auxiliary grooves451, 452 has at the rotational angle R5 a peak of the opposite phase(positive) to the cogging torque, that is, a component cancelling themain component of the cogging torque. The cancelling component isgenerated by the tooth auxiliary groove 451. Therefore, the coggingtorque of the entire motor 401 (the waveform indicated by the solidline) has a waveform in which the peak of the main component of thecogging torque at the rotational angle R5 is reduced. As describedabove, the cogging torque generated can be reduced by the toothauxiliary groove 451, and the rotation performance of the rotor 403 isimproved.

The other tooth auxiliary groove 452 operates in the same manner as thetooth auxiliary groove 451. Specifically, when the circumferentialsecond end 224 c of a salient pole 224 is aligned in the radialdirection with the circumferential second end 212 d of the opposed tooth212 (the rotational angle R6 in FIG. 23), the circumferential first end212 c of the tooth 212 is aligned in the radial direction with the outerside surface 452 b of the tooth auxiliary groove 452 of the tooth 212 f.Thus, as in the case of the tooth auxiliary groove 451 described above,the cogging torque generated by the tooth auxiliary grooves 451, 452functions as a component cancelling the peak of the opposite phase ofthe main component of the cogging torque at the rotational angle R6,that is, the main component of the cogging torque. Therefore, thecogging torque of the entire motor 401 (the waveform indicated by thesolid line) is kept low. This further reduces the cogging torque, andthe rotation performance of the rotor 403 is improved.

FIG. 24 shows the cogging torque ratio when the ratio W3/T is changed,in which W3 represents the circumferential width of the tooth auxiliarygrooves 451, 452 (see FIG. 22B) with reference to the outer sidesurfaces 451 b, 452 b located outside of the tooth auxiliary grooves452, 451, and T represents the circumferential interval T between thedistal ends of adjacent teeth 212 (see FIG. 22B), or between theprotruding portions 212 a. In FIG. 24, the cogging torque when W3/T=0,that is, the cogging torque in a configuration without the toothauxiliary grooves 451, 452, is defined as 1. As shown in FIG. 24, thecogging torque decreases as the ratio W3/T increases from 0. The coggingtorque has the minimum value (approximately 50%) when W3/T isapproximately 0.7. When W3/T increases further, the cogging torquestarts increasing from the minimum value. In the range of W3/T<1.125,the cogging torque is less than 1. That is, the cogging torque is lessthan 1 in the range of 0<W3/T<1.125. Thus, if the ratio W3/T is set to avalue in this range, the cogging torque is expected to be lowered thanthat in the case where no tooth auxiliary grooves 510, 520 are formed.If W3/T=approximately 0.7, the cogging torque is reduced toapproximately 50%. That is, the cogging torque is most significantlyreduced.

The present embodiment provides the following advantages.

(14) In the present embodiment, the tooth auxiliary grooves 451, 452 areformed in the surface 212 b of each tooth 212, and the positional angleKC3 of the tooth auxiliary grooves 451, 452 satisfies the expressionKC3=KA/2+KE−KB. Therefore, when the circumferential first end 224 b ofeach salient pole 224 is aligned in the radial direction with thecircumferential end 212 c of the opposed tooth 212 while the rotor 403is rotating, the circumferential second end 224 c of the salient pole224 is aligned in the radial direction with the side surface 451 b ofthe tooth auxiliary groove 451 of the tooth 212 e, which is adjacent tothe tooth 212 aligned with the circumferential end. Also, when thecircumferential second end 224 c of each salient pole 224 is aligned inthe radial direction with the circumferential second end 212 d of theopposed tooth 212 while the rotor 403 is rotating, the circumferentialfirst end 224 b of the salient pole 224 is aligned in the radialdirection with the side surface 452 b of the tooth auxiliary groove 452of the tooth 212 f, which is adjacent to the tooth 212 aligned with thecircumferential end. At this time the cogging torque generated by thetooth auxiliary grooves 451, 452 serves as a cancelling component thatsuppresses the main component of the cogging torque. The cogging torquegenerated in the entire motor 401 therefore can be reduced, and therotation performance of the rotor 403 is improved.

(15) In the present embodiment, the tooth auxiliary grooves 451, 452 areformed in a pair along the circumferential direction to be symmetricalwith respect to the circumferential center line H in each tooth 212.This further reduces the cogging torque.

(16) In the present embodiment, the ratio W3/T between thecircumferential width W3 of the tooth auxiliary grooves 451, 452 and theinterval T between circumferentially adjacent teeth 212 is set tosatisfy the expression 0<W3/T<1.125.,This enables further reduction inthe cogging torque (see FIG. 24), and improves the rotation performanceof the rotor 403.

The second to fourth embodiments may be modified as follows.

In the third embodiment, the auxiliary grooves 231, 232 serving as firstauxiliary grooves and the inside auxiliary grooves 341, 342 serving assecond auxiliary grooves are both provided. However, only the insideauxiliary grooves 341, 342 may be provided.

The configuration of the fourth embodiment may include the auxiliarygrooves 451, 452 of the second embodiment or the inside auxiliarygrooves 341, 342 of the third embodiment.

In the second to fourth embodiments, the auxiliary grooves 231, 232, theinside auxiliary grooves 341, 342, and the tooth auxiliary grooves 451,452 are provided in pairs. However, only one of each pair may beprovided.

The second to fourth embodiments are applied to the eight-magnetic polerotor 403 formed by four salient poles 224 and four magnets 223.However, the number of magnetic poles may be changed as necessary. Inthis case, the number of magnetic poles of the stator 202 is changed asnecessary.

A fifth embodiment of the present invention will now be described withreference to the drawings.

FIGS. 25 and 26 show an inner rotor brushless motor 501. The rotor 503used in the motor 501 of the present embodiment includes a substantiallyannular rotor core 522, seven magnets 523, and salient poles 524. Therotor core 522 is made of magnetic metal and adhered to the outercircumferential surface of a rotary shaft 521. The magnets 523 arearranged on the outer circumferential surface of the rotor core 522along the circumferential direction. Each salient pole 524 is located inthe outer circumferential portion of the rotor core 522 and between acircumferentially adjacent pair of the magnets 523. The magnets 523function as north poles. The salient poles 524 are integrally formedwith the rotor core 522. The magnets 523 and the salient poles 524 arealternately arranged on the outer circumferential portion of the rotor503 in the circumferential direction at equal angular intervals. In thepresent embodiment, each magnet 523 is located at a position oppositeto, or 180° away from, one of the salient poles 524. The rotor 503 is aconsequent pole type with fourteen magnetic poles that causes thesalient poles 524 to function as south poles in relation to the northpole magnets 523. A stator 502 is a twelve magnetic pole-type having astator core 504 with twelve teeth 512. A coil 513 is wound about eachtooth 512.

The circumferential length of each magnet 523 of the rotor 503 isslightly greater than that of each salient pole 524. Each magnet 523 issubstantially formed as a rectangular prism having a curved outsidesurface 523 a and a flat inside surface 523 b. The inside surface 523 bof each magnet 523 is fixed to a fixing surface 525 provided between acircumferentially adjacent pair of the salient poles 524 in the rotorcore 522. A first gap S1 exists between each magnet 523 and acircumferentially adjacent salient pole 524. The outside surfaces 523 aof the magnets 523 are curved and located on the same circumference.

The circumferential length of each salient pole 524 is less than that ofeach magnet 523 by the amount corresponding to the gap S1 between thesalient pole 524 and the magnet 523. Each salient pole 524 has asectoral cross section in the axial direction, and has an outsidesurface 524 a that bulges outward in the radial direction. That is, theoutside surface 524 a of each salient pole 524 is curved such that itscenter in the circumferential direction protrudes relative to both ends.In other words, the outside surface 524 a is curved such that itapproaches the radially inner end as the distance from the center in thecircumferential direction increases toward either end in thecircumferential direction. The curvature of all the outside surfaces 524a is the same, and symmetrical with respect to the circumferentialcenter.

The outside surfaces 524 a and 523 a of the salient poles 524 and themagnets 523 are arranged such that the outside surfaces 524 a of thesalient poles 524 are radially inward of the outside surfaces 523 a ofthe magnets 523. That is, in a second gap S2 between the stator 502 (thesurface (the distal surface) of the teeth 512) and the rotor 503, a gapdistance B corresponding to the salient pole 524 (in this case, theshortest gap distance at the circumferential center) is set to begreater than a gap distance A corresponding to the magnet 523 (theshortest gap distance constant in the circumferential direction).

FIGS. 27, 28, and 29 show the radial pulsation ratio, the rotorimbalance ratio, and the torque ripple ratio, respectively, when theratio B/A of the gap distance B corresponding to the salient pole 524and the gap distance A corresponding to the magnet 523 is changed in thesecond gap G2 between the stator 502 and the rotor 503. The radialpulsation, the rotor imbalance force, and the torque ripple are causesof increase in the vibration when the rotor 503 rotates.

FIG. 27 shows the radial pulsation ratio when B/A is changed. The radialpulsation when B/A=1, that is, when the gap distance B and the gapdistance A are equal to each other, is defined as 1. As B/A is increased(as the salient pole 524 is moved radially inward compared to the magnet523), the radial pulsation is reduced from 1 substantially at a constantrate. Specifically, the radial pulsation is reduced so as to beapproximately 0.89 when B/A=1.2, approximately 0.8 when B/A=1.4, andapproximately 0.72 when B/A=1.6. That is, if 1<B/A, the radial pulsationis expected to be reduced.

FIG. 28 shows the rotor imbalance force ratio when B/A is changed. As inthe above case, the rotor imbalance force when B/A=1 is defined as 1. AsB/A is increased, the rotor imbalance force decreases. Then, the rotorimbalance force starts slightly increasing after being the minimumvalue. Specifically, the rotor imbalance force decreases in the rangefrom B/A=1 to B/A=1.4. As B/A approaches 1.4, the rotor imbalance forcegradually decreases. When B/A=1.4, the rotor imbalance force has theminimum value of approximately 0.3. In the range from B/A=1.4 toB/A=1.6, the rotor imbalance force slightly increases. When B/A=1.6, therotor imbalance force increases to approximately 0.4. That is, if 1<B/A,the rotor imbalance force is expected to decreases at least when themeasured value of B/A reaches 1.6. Particularly, in the range1.25<B/A<1.6, the rotor imbalance force becomes approximately 40% orless when B/A=1. That is, the rotor imbalance is reduced significantly.

FIG. 29 shows the torque ripple ratio when B/A is changed. As in theabove case, the torque ripple when B/A=1 is defined as 1. As B/A isincreased, the torque ripple temporarily decreases. Then, the torqueripple starts slightly increasing after being the minimum value.Specifically, the torque ripple decreases in the range from B/A=1 toB/A=1.2. As B/A approaches 1.2, the torque ripple gradually decreases.When B/A=1.2, the torque ripple has the minimum value of approximately0.47. In the range from B/A=1.2 to B/A=1.6, the torque ripple increases.From B/A=1.2, the rate of increase of the torque ripple graduallyincreases. When B/A=1.55, the torque ripple becomes equal to the valuewhen B/A=1. The torque ripple continues increasing after B/A=1.55. Thatis, when 1<B/A<1.55, the torque ripple is expected to be reduced.Particularly, in the range of 1.15<B/A<1.25, the torque ripple isapproximately half the value when B/A=1. That is, the torque ripple issignificantly reduced.

Taking the above factors into consideration, in the rotor 503 of thepresent embodiment, the ratio B/A between the gap distances B and A isset to a value in the range of 1<B/A<1.55. Accordingly, the radialpulsation (FIG. 27), the rotor imbalance force (FIG. 28), and the torqueripple (FIG. 29), which are causes of vibration when the rotor 503rotates, are reduced. Particularly, to preferentially reduce the rotorimbalance force, B/A is set to approximately 1.4. To preferentiallyreduce the torque ripple, B/A is set to approximately 1.2. As describedabove, factors of vibrations during rotation of the rotor 503 arereduced, so that the rotational performance of the rotor 503 isimproved.

The present embodiment provides the following advantages.

(17) In the gap S2 between the stator 502 and the rotor 503 of thepresent embodiment, the ratio B/A between the gap distance A, whichcorresponds to the magnets 523, and the gap distance B, whichcorresponds to the salient poles 524 is set to an appropriate value thatsatisfies 1<B/A. This reduces the radial pulsation, the rotor imbalanceforce, and the torque ripple, which are causes of vibration when therotor 503 rotates (see FIGS. 27 to 29), thereby improving the rotationalperformance of the rotor 503. That is, it is possible to provide a motor501 of an improved rotation performance.

By setting the ratio B/A of the gap distances A and B to any value inthe range of 1.25<B/A<1.6, the rotor imbalance force can be effectivelyreduced in addition to the reduction in the radial pulsation.

Also, by setting the ratio B/A of the gap distances A and B to any valuein the range of 1<B/A<1.55, the torque ripple can be effectively reducedin addition to the reduction in the radial pulsation. In this case, bysetting the ratio B/A of the gap distances A and B to any value in therange of 1.15<B/A<1.25, the torque ripple can be further effectivelyreduced.

Also, by setting the ratio B/A of the gap distances A and B to any valuein the range of 1.2<B/A<1.4, both of the rotor imbalance force and thetorque ripple can be effectively reduced in addition to the reduction inthe radial pulsation.

(18) In the present embodiment, the number of the magnets 523 and thenumber of the salient poles 524 are both an odd number, and each magnet523 is at a position opposite to, or 180° away from, one of the salientpoles 524. That is, in a configuration in which each magnet 523 is at aposition opposite to, or 180° away from, one of the salient poles 524,magnetic imbalance is likely to occur and the vibration during rotationof the rotor 503 is likely to increase. Thus, the optimization of theratio B/A of the gap distances A and B is significant in reducing thevibration.

The above described fifth embodiment may be modified as follows.

In the fifth embodiment, the shapes of the outside surfaces 524 a and523 a of the salient poles 524 and the magnets 523 may be changed asnecessary. In the first embodiment, the outside surfaces 523 a of themagnets 523 are arcuate and arranged on the same circle, and the outsidesurface 524 a of each salient pole 524 has a greater curvature than thatof the outside surface 23 a. Also, the outside surfaces 524 a, 523 a maybe curved and located on the same circle. Further, the outside surfaces524 a, 523 a may be curved to have a large curvature. The curvature ofthe outside surfaces 524 a, 523 a does not need to be constant, but maybe changed along the circumferential direction or changed linearly.

Other than these modifications, the shape of the magnets 523 and theshape of the rotor core 522 including the salient poles 524 may bechanged as necessary.

The first to fifth embodiments may be modified as follows.

The ranges of the values in each embodiment may be changed as necessarydepending on the conditions.

In the above illustrated embodiments, coils of the stators 2, 202, and502 are formed by segment coils 13. Instead, continuous wires may bewound about the teeth 12.

In the above illustrated embodiments, the present invention is appliedto the inner rotor type motors 1, 100, 400, 500. However, the presentinvention may be applied to an outer rotor type motor.

In the above illustrated embodiments, the shapes of the magnets 23, 223,523 and the shapes of the rotor cores 22, 222, 522 including the salientpoles 24, 224, 524 may be changed as necessarily.

The above illustrated embodiments are configured such that the magnets23, 223, 523 function as north poles, and the salient poles 24, 224, 524function as south poles. However, a configuration may be employed inwhich the magnets 23, 223, 523 function as south poles, and the salientpoles 24, 224, 524 function as north poles.

The number of magnetic poles may be changed as necessary in the aboveillustrated embodiments. In this case, the number of magnetic poles ofthe stators 2, 202, 502 is changed as necessary.

1. A motor comprising: a rotor including: a rotor core; a plurality ofmagnets arranged along the circumferential direction of the rotor core,the magnets functioning as first magnetic poles; and a plurality ofsalient poles integrally formed with the rotor core, each salient polebeing located between a circumferentially adjacent pair of the magnetswith gaps in between, and functioning as a second magnetic poledifferent from the first magnetic poles; and a stator arranged to beopposite to the rotor with a gap along the radial direction, wherein thegap is set to satisfy an expression 1<B/A, where A represents theshortest gap distance between the stator and the magnets, and Brepresents the shortest gap distance between the stator and the salientpoles.
 2. A motor according to claim 1, wherein the ratio B/A is in therange of 1.25<B/A<1.6.
 3. A motor according to claim 1, wherein theratio B/A is in the range of 1<B/A<1.55.
 4. A motor according to claim3, wherein the ratio B/A is in the range of 1.15<B/A<1.25.
 5. A motoraccording to claim 1, wherein the ratio B/A is in the range of1.2<B/A<1.4.
 6. A motor according to claim 1, wherein the number of themagnets and the number of the salient poles are each an odd number, andwherein each magnet is located at a position opposite to, or 180° awayfrom, one of the salient poles.